Frequently, excessive voltage or current is applied across service lines that deliver power to residences and commercial and institutional facilities. Such excess voltage or current spikes (transient overvoltages and surge currents) may result from lightning strikes, for example. The above events may be of particular concern in telecommunications distribution centers, hospitals and other facilities where equipment damage caused by overvoltages and/or current surges and resulting down time may be very costly.
Typically, sensitive electronic equipment may be protected against transient overvoltages and surge currents using Surge Protective Devices (SPDs). For example, brief reference is made to FIG. 1, which is a system including conventional overvoltage and surge protection. An overvoltage protection device 10 may be installed at a power input of equipment to be protected 50. The overvoltage protection device 10 may include a surge protection device 12. When a surge current Isurge flows towards the equipment 50, the surge protection device 12 may conduct a portion thereof (ISPD), leaving a surge current portion IEQ that flows through the equipment 50.
However, there are applications where the immunity level of the sensitive electronic equipment to be protected against transient overvoltages and surge currents is very low. In such cases, the residual voltage of the SPD (VSPD) or the portion of the surge current that flows to the electronic equipment (IEq) may exceed the immunity level (resistibility) of the equipment to overvoltages and/or surge currents and may result in damage thereto.